In response to the requirement of higher data transfer rate as requested by the future communication system, the methods for increasing the data transfer rate have been extensively discussed. For example, the co-time co-frequency full duplex (CCFD) technology is provided, and may even be included in the fifth generation (5G) standards for mobile communications. In the CCFD system, two communication devices can exchange data at the same time using the same frequency. In theory, the spectrum efficiency of the CCFD system is double than that of the conventional duplexing system.
However, in the CCFD system, self-interference will occur when the communication device is transmitting or receiving signals, and will therefore reduce the signal-to-noise ratio (SNR). Self-interference is particularly strong when the communication device is farther away from the base station device and needs to use a larger amount of energy to maintain the quality of signals transmitted between the communication device and the base station device. If the communication device increases the amount of energy when transmitting signals, signal self-interference will be increased at the same time, and normal operation of CCFD system cannot be maintained.